The information recording and reading-out apparatuses using light is advancing toward increase of capacity and decrease of size, requiring recording bit density increase. As a countermeasure there are studies using violet semiconductor lasers or SIL (Solid Immersion Lens). With these technologies, expectable improvement is at most nearly several times the current recording density because of a problem with diffraction limit of light. Contrary to this, there is an expectation for an information recording and reading-out method utilizing near-field light as a technology dealing with optical information in very small area exceeding the light diffraction limit.
This technology utilizes near-field light caused due to the interaction between a very small area and an optical aperture formed in a size less than a wavelength of light in a near-field optical head. This makes it possible to deal with optical information in the region of less than a light wavelength as a limit in the conventional optical system. The optical information reading-out methods include a method of illuminating scattering light onto a media surface to convert a greater part of near-field light localized at a very small mark into propagation light through the interaction with the very small aperture (collection mode), and a method of illuminating near-field light produced through an very small aperture onto a media surface thereby detecting, by a separately provided detector, scattering light converted through an interaction with a microscopic concave-convex having information recorded on a media surface (illumination mode). Recording is made by illuminating the near-field light produced from the very small aperture to a media surface thereby changing the form of a very small area on the media (heat mode record) or by changing the refractivity or transmissivity in a very small area (photon mode record). By using these near-field optical heads having the optical very small aperture exceeding a light diffraction limit, recording bit density increase can be achieved exceeding beyond the conventional optical information recording and reading-out apparatuses.
In such situations, generally the recording and reading-out apparatuses utilizing near-field light are almost similar in structure to the magnetic disk apparatus, and employ a near-field optical head in place of a magnetic head. The near-field optical head with an optical very small aperture mounted at a tip of a suspension arm is floated to a given height by a flying head technology and accessed to an arbitrary data mark existing on the disk. In order to follow up the near-field optical head to high-speed rotation of the disk, a flexture function is provided to stabilize the position coping with winding on the disk.
In the near-field optical head thus constructed, the method of supplying light to the aperture adopts means of connecting an optical fiber from above directly to the head or directly illuminating a laser provided above a head onto the head.
Also, in place of the near-field optical head, an optical fiber probe or cantilever-type optical probe sharpened at an aperture part formed by an optical fiber represented in a near-field optical microscope is used to achieve information recording and reading-out through an interaction by a tunnel current or interatomic force caused between a probe and a media surface of a scanning probe microscope while keeping a relative position to the media.
Meanwhile, there is a proposal of using a planar probe having an inverted pyramid structured aperture formed in a silicon substrate by anisotropic etching. Light is incident from above and then reflected upon the inverted conical pyramid thereby causing near-field light through the aperture present at an apex thereof. This prove does not have a sharpened tip as mentioned above and hence can be used as an optical head suited for high speed recording and reading-out.
However, if light is incident with a structure connected an optical fiber from above, an optical fiber structure is in connection between the head and the arm to thereby preventing the head from moving freely. Thus, the head is difficult to control in position relative to disk motion. Further, the head structured in large size makes it impossible to maintain a distance between the disk and the aperture. This results in a situation that the output SN ratio from optical information depicted on the disk is lowered thus making it difficult to read and write signals. Meanwhile, the greater part of light attenuates before reaching the aperture thus making it difficult to produce sufficient near-field light from the aperture for implementing reading-out at high speed. Furthermore, the structure having the upwardly extending fibers increases the size of apparatus itself making difficult to reduce the size and thickness thereof. Also, the optical fibers are inserted in and positioned one by one on the head thus being short in mass producibility.
Meanwhile, where illuminating a signal by a laser arranged above the head directly onto the head, there is a need of coping with high speed movement of the head to synchronize light to be incident thereon. There is a necessity of separately providing a structure that moves responsive to movement of the head thus encountering difficulty. Also, the separate provision of such a structure increases the size of the apparatus itself and the size reduction of the reading-out and recording apparatus is difficult.
Furthermore, where keeping constant a distance to a media through the interaction with a media surface by use of an optical fiber probe having optical fiber sharpened at its tip or a cantilever-type optical probe sharpened at its tip, scanning should be made while controlling a distance to the media at all times. This requires a feedback apparatus therefor and making difficult to reduce the size of the recording and reading-out apparatus. Furthermore, there is also a problem in high speed scanning because of a limitation of response speed of the feedback system. Also, the tip-sharpened probe is not sufficient in mechanical strength and hence not suited for being arrayed. Also, the intensity of near-field light from the aperture is not sufficient due to light loss at a fiber tip. Also, the probe is manually fabricated one by one and lack in mass producibility.
Meanwhile, the planar probe requires light to be incident from above thus posing a problem with apparatus size increase and mass producibility or a problem with reduction in flexture function as encountered in the above problem.
Furthermore, the probe aperture must be formed in a size smaller than a wavelength of propagation light (laser light, etc.) in order to produce near-field light or scatter near-field light. it is however difficult to fabricate such a size (10 nano-meters to 200 nano-meters) of an aperture to an objective shape and size with accuracy and reproducibility.
For example, in the planar probe, etching is usually conducted for making in a silicon substrate a very small aperture suited for producing or scattering near-field light. There are cases of encountering problems concerning silicon substrate quality or etch solution concentration nonuniformity.
In concerned with silicon substrate quality in the former case, the periodic existence of silicon crystalline surfaces are premised for a method of forming a taper by anisotropic etching to open a hole penetrating the silicon substrate or a method of causing an aperture to appear by isotropically etching (etch-back) at an backside of the silicon substrate forming a taper. This results in unetching in a direction or at a rate as intended in areas containing crystalline defects or impurities, causing errors in the shape or size of a finally available aperture.
Meanwhile, the problem with etch solution concentration nonuniformity in the latter case means that there is more or less nonuniformity of concentration in an etch solution and such concentration nonuniformity causes an area that etching advances at a high rate and that advances at a low rate on a silicon substrate, i.e. there appear areas different in etch rate resulting in causing errors in the shape or size of a finally obtained aperture. Such a problem cannot be neglected particularly for a case where a multiplicity of planar probes are to be formed on a silicon wafer, thus posing a cause of incurring reduction of yield.
Accordingly, it is an object of the present invention to provide, in a near-field optical head having a very small aperture for producing near-field light, a near-field optical head which is capable of producing near-field light sufficiently greater than the aperture and obtaining reading-out and recording with resolution, compact in structure and excellent in mass producibility and arraying with two dimensional arrangement, capable of stably recording and reading-out due to movement following a media without hindering a flexure function, capable of recording and reading-out at high speed and being reduced in size and thickness.